1. Field of the Invention
The present invention is directed to a polymer feed assembly or polymer activation system for feeding polymer (dry, liquid, or emulsified) to a mixing chamber and mixing the polymer with a predetermined amount of an electrolyte to activate the polymer. The present invention is specifically designed to avoid premature activation of the polymer along the polymer supply line or at the polymer/water contact site, as well as at any subsequent conduits to avoid clogging or bridging of the polymer input line at these sites. The present invention includes a purging mechanism whereby unwanted moisture or polymer is removed from the polymer feed assembly in order to avoid or prevent clogging.
2. Background and Description of the Related Art
Polymers activated through a polymer feed assembly may be used in a variety of applications, including: water purification and flocculation; automotive paint spray booths; in the chemical industry to separate inorganics and solids from effluent; in the coal industry to promote solids settling and to float coal fines; in the petrochemical industry to enhance oil recovery; in the phosphate industry to improve recovery; in the pulp and paper industry as dewatering aids and retention aids; or in the steel industry to settle waste. This list is by no means all inclusive. An example of a polymer that is typically used in these industries is polyacrylamide. Another example is a copolymer of acrylamide with an anionic molecule such as acrylic acid. The polymers, whether in dry, liquid or emulsion form, are ionic-charged organic molecules which are soluble in an electrolytic fluid such as water. The terms electrolytic fluid, solvent, and water will be referred to interchangeably herein, but retain their respective definitions where specifically noted.
Usually polymers utilized in these applications are manufactured and shipped in a deactivated form to a location where they will be utilized. At that location, it is necessary to activate the polymers before they can be used for their intended purpose. U.S. Pat. No. 5,407,975 and U.S. Pat. No. 5,470,150, both of which are hereby incorporated herein by reference, are examples of polymer activating systems known in the art.
For a dry polymer, initial activation requires more energy and time because there is no water present. In addition, the energy required for activation increases with increasing particle size. Liquid polymers are defined as polymers already dissolved to some extent in water. Although activation is easier tor liquid polymers than dry polymer, the viscous nature of the liquid polymer makes handling (e.g. pumping) of the liquid polymer difficult. Polymers in emulsion form have a relatively low viscosity when compared to liquid polymers, and therefore are easier to handle. Emulsified polymers also activate easier than dry polymers because of the small size of polymer particles. Another advantage of emulsified polymers is that they provide higher polymer concentration than liquid form.
Emulsified polymers have numerous advantages over other unactivated polymer forms. An emulsion polymer normally consists of polymer, either in dry form or liquid form in an inactive state, encased in an oil phase. The hydrocarbon surroundings of the inactive polymer must be broken down to allow water to contact the polymer in order to activate and invert the polymer. Further activation is required to allow further hydration (e.g. the penetration of more water), as well as the uncoiling of the molecule. Once the molecules begin to repel each other, the polymer molecule straightens and changes from a substantial coil shape into a long and substantially straight conformation. Once the molecules begin to repel each other, the polymer is considered to be in activated form.
Once activated, the polymer molecules can perform their intended function. An example of such a function is flocculation. Inadequate activation may result in loss of efficiency in the intended use of the polymer. In addition, the activation process must be designed precisely so as to successfully change the original state of the concentrated emulsified polymer into a diluted activated form at a predetermined concentration. Poor activation results in a polymer which is inefficient and may result a material consistency that is difficult for purposes of material handling (i.e. a more viscous material), and may result in a polymer that cannot be further activated, and may result in clogging or bridging in the system.
The related art generally uses either batch or continuous feeding methods to activate emulsified polymers. In both batch and continuous methods, polymer and water are delivered to a polymer/water contact site where they may be activated. The polymer/water contact site is usually part of a mixing chamber. The mixing chamber can be of any dimension or form as long as it brings the emulsified polymer and water together. An eductor is an example of a mixing chamber where stored energy in the water in the form of pressure is released and imparted to the molecules of water and polymer entering into the eductor. A static mixer is another example of a mixing chamber. Activation continues in the mixing chamber and subsequent conduits. In a batch system, the polymer is further activated by aging in a tank where the partially activated polymer is mixed with an impeller or mixed by recirculation or alternatively simply left standing. In a continuous system, the polymer is further activated by: introducing a significantly larger volume of solution into the system with or without the use of static shearing devices (generally known as static mixers); imparting energy via recirculation of part of the system through a pump, or a mixer, or any moving or static shearing devices; or imparting energy by passing through (once-through without recirculation) a contained volume with a mixer or any moving or static shearing device. The mixing chamber can be either inside or outside the recirculating system or the contained volume described above.
One of the major problems of the related art is the occurrence of clogging or bridging of polymer within the polymer supply line or near the point where the polymer supply line enters the mixing chamber (this may be referred to herein as the polymer/water contact site) or at subsequent conduits. Unwanted activation of the emulsified polymer is caused by moisture entering into the polymer supply line and is exacerbated by a general funnel shape of the polymer supply line at or near the point where the polymer enters the mixing chamber. The funnel shape often results from an attempt to minimize the backflow of water by minimizing, the area of contact between polymer and water at the polymer/water contact site. Also, due to the viscosity of the polymer, the cross sectional area of the polymer supply line is generally larger than the cross sectional area of the polymer/water contact site. This results in a funneling of the polymer supply line at or near the input port of the mixing chamber. Although the funneling is intended to minimize unwanted activation, once activated, the funneling area is clogged with partially activated polymer.
Clogging of the polymer supply line is the result of unwanted or premature activation of an emulsified polymer anywhere in the polymer supply line other than the polymer/water contact site or mixing chamber.
Clogging in the mixing chamber and subsequent conduits (i.e., recirculation or dispensing conduits) is usually caused by: the propagation of the prior clogging from the polymer supply line; the loss of activation energy (mixing energy) in the mixing chamber and subsequent areas; or the loss of adequate quantity of water in these areas. Loss of imparted energy and loss of water supply are often the result of natural unpredictable malfunction of equipment.
Unwanted activation often results from inherent characteristics of the polymer or operational methodology of the activation system. Known factors that intensify unwanted activation are: higher concentration of active polymer in the emulsified polymer; higher molecular weight (larger molecules) of the polymer, polymer material that has a higher affinity for water (hydrophyllic); and periodic shut-downs of the assembly. Down times for the emulsion feed assembly are particularly bad for clogging purposes because the emulsified polymer is no longer in motion.
Unwanted or pre-mature activation is also an inherent property of the polymer due to the abundant presence of water or moisture. As mentioned above, precise design features are required to prevent this unwanted contact of the emulsified polymer with water other than at the polymer/water contact site or in the mixing chamber. Examples of such preventative designs include a valve inserted between the polymer supply line and the polymer/water contact site and a funnel-shaped conduit. In the related art funnel-shape at the end of the polymer input line minimizes backflow because the area of contact at the polymer/water contact site is minimized.
Regardless of how precise the design is, small amounts of water or moisture may start the propagation or unwanted activation of the emulsified polymer. Unwanted activation results in a very viscous material which begins to partially clog the polymer supply line and valves. With time, the quantity of viscous material increases, often resulting in unscheduled down time for repair and cleaning of the feed assembly.